In recent years, polymers having a main chain of cyclic hydrocarbon skeleton are drawing attention as a polymer material which is superior in heat resistance and mechanical strengths owing to the rigid structure and further superior in optical properties, electrical properties, etc. Such polymers are classified into two groups from the main chain structures which affect the properties. The first group is norbornene type compound metathesis polymers (see, for example, the third chapter of “Synthesis of Polymers” by R. H. Grubbs, published from Wiley VCH in 1999). These polymers have a structural feature of having spacer moieties of chain skeleton between units of bulky cyclic skeleton. The second group is polymers constituted by a cyclic skeleton alone and having no spacer moiety. They are, for example, a norbornene type compound vinylene-type polymer (see, for example, JP-A-3205408, JP-4-63807 and JP-A-5-262821); a cyclopentene polymer (see, for example, JP-A-3-139506, WO 99/50320, and “Macromolecules” 1998, 31, 6705); a cyclopentadiene polymer (see, for example, “Macromolecules” 2001, 34, 3176); and a 1,3-cyclohexadiene polymer (see, for example, JP-A-7-247321, JP-A2000-26581 and JP-A-2000-351885). However, polymers which are sufficient in practical performances of solubility in solvents, heat resistance, mechanical strengths and the like have not been developed yet.
Of these polymers, the 1,3-cyclohexadine polymer has a high glass transition temperature of 170° C. and a high solubility in solvents and is hopeful as a next-generation resin. However, the polymer has a rigid cis structure and is bulky three-dimensionally, and accordingly the polymerization process for production thereof is limited. Recently, there have been developed polymerization processes such as anionic polymerization using a butyl lithium/tetramethylethylenediamine catalyst (see, for example, JP-A-7247321), nickel catalyst coordination polymerization (see, for example, JP-A2000-26581, JP-A-2000-351885, and “Chemical Communications” 2000, 22072208), and the like; however, the catalysts used therein are still limited. Further, 1,3-cyclohexadiene per se is difficult to produce industrially. For example, dehydrogenation of cyclohexene (see, for example, JP-A-7-196737) is inferior in conversion and selectivity and has a difficulty in separation of byproducts; further, it has a detrimental drawback in that there is by-produced 1,4-cyclohexadiene which impairs polymerization of 1,3-cyclohexadiene. There is also a process for producing 1,3-cyclohexadiene via cyclohexene chloride (see, for example, JP-A-11-189614); however, this process employs several steps and moreover gives a low yield and, therefore, is far from satisfaction industrially.
Hence, the first object of the present invention is to provide a cyclic diene polymer which is produced from a cyclic conjugated diene monomer easy to produce and high in polymerization activity, additionally has high heat resistance and high mechanical strengths and shows good solubility in solvents.
Olefins having a cyclic hydrocarbon skeleton are used as a raw material for the above-mentioned polymers of high performances. By using, in particular, a cyclic diolefin, the polymer obtained can be imparted with further functions. For example, a cyclic non-conjugated diolefin such as dicyclopentadiene, vinylnorbornene, ethylidenenorbornene or the like has two kinds of unsaturated bonds of different reactivity; therefore, polymerization is possible with one unsaturated bond and functions can be imparted with the other unsaturated bond. In the case of, for example, ethylidenenorbornene which is widely used industrially as the third component of ethylene/propylene/diene rubber (EPDM) [see, for example, pp. 120 to 122 of “Basis of Rubber Technology (New Edition)” published from The Society of Rubber Industry, Japan on 2002, and pp. 130 to 139 of “Handbook of Rubber Industry (New Edition)” published from The Society of Rubber Industry, Japan on 1994], it is considered that the unsaturated bond of norbornene ring reacts during copolymerization and the unsaturated bond of ethylidene group reacts during vulcanization of rubber. When a difference in reactivity between two kinds of unsaturated bonds is utilized, however, with the result that the difference is not sufficiently large, the two unsaturated bonds may react during polymerization to form a three-dimensional crosslink, which may cause gelling.
Meanwhile, a conjugated diene compound is characterized in that the polymer obtained therefrom contains remaining unsaturated bonds always. The remaining unsaturated bonds are utilized for secondary reaction such as crosslinking, vulcanization or the like, or for imparting functions by chemical conversion such as hydrogenation, epoxidization, halogenation, arylation, hydration, carbonylation or the like.
Of various conjugated diene compounds, compounds having a cyclic hydrocarbon skeleton, i.e. cyclic conjugated dienes are expected as a very useful compound; however, examples of such cyclic conjugated dienes are very few and only 1,3-cyclohexadiene or so is mentioned (see Macromolecular Chemistry and Physics, U.S., 2001, 202, pp. 409 to 412, and Journal of Polymer Science: Part B: Polymer Physics, U.S., 1998, Vol. 36, pp. 1657 to 1668). Moreover, as mentioned above, the 1,3-cyclohexadiene per se is difficult to produce industrially.
Thus, there is strongly desired, for its industrial usefulness, a copolymer which is obtained by copolymerization of a cyclic conjugated diene of high polymerizability and easy production with other unsaturated compound.
Hence, the second object of the present invention is to provide a cyclic diene copolymer obtained by copolymerization of a cyclic conjugated diene monomer of easy production and high polymerization activity, with an unsaturated compound.